Sometimes they get a short under the hood fuse box. The wires rub against the support brackets.
Of course the NSBU switch can always be a problem with the LLY. But without communication-- that cannot be the issue.
Some do have ignition switch problems-- but easy to check with a test light or volt meter.
Chevy 04.5 LLY, 2X, shell, XDR, MikeL Heavy duty up-grade, 6spd, TransGo, deep pan, de-badged, 65 Gallon replacement Aero tank, LBZ-mp, Kennedy pump, shimmed, Pre-fuel filter, tow mirrors, BU cam, gauges, GPS, Sirius, bags, custom grille, fender vents, HD trans cooler- Curt front hitch, footwell lights, load lights, Studs, head gaskets.--- Jerry